The present invention generally relates to solenoid valves, and more particularly to an improved solenoid valve which varies the rate at which hydrocarbons can be removed from an evaporation canister and re-enter the intake manifold of an engine.
To eliminate the flow of hydrocarbons into the atmosphere, internal combustion engines use an evaporation canister which stores hydrocarbon vapors from within the engine and the fuel tank. Upon restarting the engine, the free hydrocarbons within the evaporation canister are returned to the intake manifold. In order to prevent an excessive amount of hydrocarbons from appearing in the exhaust when the engine is started, the rate at which the hydrocarbons are permitted to flow from the canister into the intake manifold is controlled by an electrically operated canister purge valve. Such valve can be of a normally closed or normally open variety. Normally open valves found in the prior art which remain open when no power is applied thereto require the use of a check valve to prevent vapor from flowing into the atmosphere while the engine is not running. The normally closed solenoid valve obviates the need for a check valve since such valves remain closed until control signals are communicated to the solenoid. However, the failure of such normally closed valves will cause the emission control system to fail to meet evaporative emission requirements by not being able to open and close at proper times.
It is an object of the present invention to eliminate those deficiencies found in the prior art. A further object of the present invention is to provide an automatically opening canister purge solenoid operated valve which is capable of a maximum flow of approximately 2.0 standard cubic feet per minute (56,634 cubic millimeters per minute) of air at a pressure differential of 10 inches (25.4 centimeters) of mercury.
A further object of the present invention is to provide a canister purge valve which opens automatically under the influence of intake manifold pressure thereby ensuring that hydrocarbons within the evaporation canister can be combusted within the engine regardless of the operable condition of an electrically energized coil.
A further object of the present invention is to provide a valve which is normally closed in the absence of any external influences.
A further object of the present invention is to provide a valve in which the rate at which hydrocarbons are permitted to re-enter the intake manifold is variable and electrically controlled.
Another object of the present invention is to provide a low cost, repeatably operating solenoid activated valve having an improved magnetic circuit.
Many other objects, purposes, features and advantages of the invention will be clear from the detailed description of the drawings.
Accordingly, the invention comprises a canister purge valve comprising a housing including a vacuum chamber communicated to an axially extending vacuum port and an opening; an assembly received within the housing including a valve seat positioned within the vacuum chamber. The assembly further including an axially extending outlet port extending through the opening in the housing and a plurality of passages communicating the outlet port to the vacuum chamber, the valve further including means for providing a seal between the housing and the assembly proximate the vacuum chamber, valve means movably positioned within the vacuum chamber for seating upon the valve seat for opening and closing communication between the inlet port and the outlet port, means for biasing the valve means against the valve seat, and means for generating a magnetic flux signal in response to control signals for urging the valve means to seat upon the valve seat.